Message-ID: <41594180.3010906@yahoo.com.au>
Date: Tue, 28 Sep 2004 20:48:32 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Ingo Molnar <mingo@elte.hu>
CC: "J.A. Magallon" <jamagallon@able.es>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, tytso@mit.edu
Subject: Re: Stack traces in 2.6.9-rc2-mm4
References: <6.1.2.0.2.20040927184123.019b48b8@tornado.reub.net> <20040927085744.GA32407@elte.hu> <1096326753l.5222l.2l@werewolf.able.es> <20040928072123.GA15177@elte.hu> <4159177F.7030803@yahoo.com.au> <20040928102454.GA20271@elte.hu>
In-Reply-To: <20040928102454.GA20271@elte.hu>
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Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
> 
>>>+	preempt_disable();
>>>	/* if over the trickle threshold, use only 1 in 4096 samples */
>>>	if ( random_state->entropy_count > trickle_thresh &&
>>>	     (__get_cpu_var(trickle_count)++ & 0xfff))
>>>-		return;
>>>+		goto out;
>>>
>>
>>It looks like upstream code *is* buggy because that is a non-atomic
>>RMW operation on the per-cpu var, no? Hence you must disable preempt.
> 
> 
> no, the upstream code (i.e. BK-curr) is not buggy, because there this
> code runs under the BKL, implicitly as part of vt_ioctl() - and the BKL 
> disables preemption in the upstream kernel.
> 
> Yes, the code is fragile, but it's not buggy. With the remove-bkl patch
> this fragility turned into an outright bug. (Fortunately the patch
> detects all such incidents.)
> 

Ahh yeah you're right, sorry.
-
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